The transparent patterned electrically conducting electrodes of electro-optical displays (LCD, Electroluminescent) are generally supported on transparent support plates or substrates. The electrodes are usually prepared by first coating one surface of the substrate, for example, by vapor deposition or sputtering in vacuo, with a continuous thin film of a transparent, electrically conducted material, for example semiconductive metal oxide such as indium oxide and/or tin oxide, and then selectively removing portions of the deposited film by etching to produce an electrode pattern. As freshly deposited, that is without heat treatment, the vapor deposited or sputtered films can be etched relatively easily with acids. In order to confine the etching to selected areas, the film is covered with a photoresist, which is a layer of photopolymerizable material. The photoresist is then polymerized imagewise by exposure to actinic radiation. The unpolymerized resist in the unexposed areas can then be removed, for example by a suitable solvent, to form the windows of an etching mask. Subsequently, the uncovered areas of the transparent electrically conductive film are etched away, and the photoresist layer is removed from the covered areas of the transparent electrode film, which remain on the substrate (See U.S. Pat. No. 4,348,255). The photoresist etching process makes it possible to prepare very complex electrode patterns and those having very fine lines, especially in thin film electroluminescent displays which normally require delineation of a perfect pattern of hundreds of column electrodes over an area of thousands of square centimeters. However, the transparent electrode material is difficult to etch and the etchant (for example hydrochloric or hydrobromic acids) attacks both the photoresist etch mask and the glass substrate. The etching process also tends to leave sharp, ragged edges on the conductor patterns which produce weak areas in the subsequently deposited layers and eventually cause device breakdown. In addition, variability in glass substrate flatness, semiconductive metal oxide film thickness and photoresist thickness causes this process to require a great deal of technical judgment at critical steps and consistently results in electrode patterns that are not sufficiently delineated to be commercially acceptable.
Therefore, a need has continued to exist for a method of producing patterned transparent electrodes on substrates which avoid the problems introduced by known methods of etching.